Instruments and methods for bone anchor engagement and spinal rod reduction

ABSTRACT

An instrument for engaging a bone anchor may include a first implant engaging member having a proximal end and a distal end and a second implant engaging member having a proximal end and a distal end. The second implant engaging member may be integrally connected to the first implant engaging member by a pair of opposed integral spring members located proximal to the distal ends of the first and second implant engaging members. Manipulation of the proximal ends of the first and second implant engaging member can cause each of the distal ends to rotate about the pair of opposed spring members to engage at least a portion of a bone anchor. A rod adjusting tool may be connectable to the bone anchor engaging tool and may be axially adjustable relative to the bone anchor tool to adjust a spinal rod relative to the bone anchor.

REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 11/235,694, filed Sep. 26, 2005, which is acontinuation-in-part of U.S. patent application Ser. No. 11/013,180,filed Dec. 15, 2004, and is a continuation-in-part of U.S. patentapplication Ser. No. 11/013,258, filed Dec. 15, 2004. U.S. patentapplication Ser. No. 11/013,180 and U.S. patent application Ser. No.11/013,258 each claim the benefit of U.S. Provisional Application No.60/530,179, filed on Dec. 17, 2003. Each of the aforementioned patentapplications is hereby incorporated by reference.

BACKGROUND

Spinal fixation systems may be used in orthopedic surgery to alignand/or fix a desired relationship between adjacent vertebral bodies.Such systems typically include a spinal fixation element, such as arelatively rigid fixation rod or plate, that is coupled to adjacentvertebrae by attaching the element to various anchoring devices, such ashooks, bolts, wires, or screws. The spinal fixation element can have apredetermined contour that has been designed according to the propertiesof the target implantation site, and once installed, the spinal fixationelement holds the vertebrae in a desired spatial relationship, eitheruntil desired healing or spinal fusion has taken place, or for somelonger period of time.

Spinal fixation elements can be anchored to specific portions of thevertebra. Since each vertebra varies in shape and size, a variety ofanchoring devices have been developed to facilitate engagement of aparticular portion of the bone. Pedicle screw assemblies, for example,have a shape and size that is configured to engage pedicle bone. Suchscrews typically include a threaded shank that is adapted to be threadedinto a vertebra, and a head portion having a spinal fixation elementreceiving element, which, in spinal rod applications, is usually in theform of a U-shaped slot formed in the head for receiving the rod. Aset-screw, plug, cap or similar type of closure mechanism, is used tolock the rod into the rod-receiving portion of the pedicle screw. Inuse, the shank portion of each screw is then threaded into a vertebra,and once properly positioned, a fixation rod is seated through therod-receiving portion of each screw and the rod is locked in place bytightening a cap or similar type of closure mechanism to securelyinterconnect each screw and the fixation rod. Other anchoring devicesalso include hooks and other types of bone screws.

While current spinal fixation systems have proven effective,difficulties have been encountered in mounting rods into therod-receiving portion of various fixation devices. In particular, it canbe difficult to align and seat the rod into the rod receiving portion ofadjacent fixation devices due to the positioning and rigidity of thevertebra into which the fixation device is mounted. Thus, the use of aspinal rod approximator, also referred to as a spinal rod reducer, isoften required in order to grasp the head of the fixation device andreduce the rod into the rod-receiving portion of the fixation device.

While several rod approximators are known in the art, some tend to bedifficult and very time-consuming to use. Accordingly, there is a needfor an improved rod approximator and methods for seating a spinal rod ina rod-receiving portion of one or more spinal implants.

SUMMARY

Disclosed herein are instruments that facilitate the engagement of aninstrument, such as a reduction instrument or approximator, to animplant such as a bone anchor. In one exemplary embodiment, aninstrument for engaging a bone implant may comprise a first implantengaging member having a proximal end and a distal end and a secondimplant engaging member having a proximal end and a distal end. Thesecond implant engaging member may be integrally connected to the firstimplant engaging member by a pair of opposed integral spring memberslocated proximal to the distal ends of the first and second implantengaging members. In use, manipulation of the proximal ends of the firstand second implant engaging members can cause each of the distal ends torotate about the pair of opposed spring members to engage at least aportion of an implant.

In another exemplary embodiment, a rod reduction instrument foradjusting a spinal rod relative to a bone anchor may comprise a boneanchor engaging tool and a rod adjusting tool. The bone anchor engagingtool may include a first jaw member having a proximal end and a distalend and a second jaw member having a proximal end and a distal end. Thesecond jaw member may be integrally connected to the first jaw member bya pair of opposed integral spring members located proximal to the distalends of the first and second jaw members. In use, manipulation of theproximal ends of the first and second jaw members can cause each of thedistal ends to rotate about the integral spring members to engage atleast a portion of a bone anchor. The rod adjusting tool, in theexemplary embodiment, may be connectable to the bone anchor engagingtool and may have a proximal end and a distal end. The rod adjustingtool may be axially adjustable relative to the bone anchor tool toadjust a spinal rod relative to the bone anchor.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the instruments and methodsdisclosed herein will be more fully understood by reference to thefollowing detailed description in conjunction with the attached drawingsin which like reference numerals refer to like elements through thedifferent views. The drawings illustrate principles of the instrumentsdisclosed herein and, although not to scale, show relative dimensions.

FIG. 1 is a perspective view of an exemplary embodiment of an instrumentfor adjusting a spinal rod relative to a bone anchor, illustrating a rodadjusting tool positioned within a bone anchor engaging tool;

FIG. 2 is a side elevational view of the instrument of FIG. 1;

FIG. 3 is a top view of the instrument of FIG. 1;

FIG. 4 is a perspective view of the bone anchor engaging tool of FIG. 1;

FIG. 5 is a side elevational view of the bone anchor engaging tool ofFIG. 4, illustrating the jaw members of the tool in an approximatelyclosed position;

FIG. 6 is a side elevational view in cross-section of the bone anchorengaging tool of FIG. 4, illustrating the jaw members of the tool in anapproximately closed position;

FIG. 7 is a side elevational view of the interior surface of a jawmember of the bone anchor engaging tool of FIG. 4;

FIG. 8 is a side elevational view of the exterior surface of a jawmember of the bone anchor engaging tool of FIG. 4;

FIG. 9 is a side elevational view in cross-section of the jaw member ofFIG. 4, taken along line 9-9 of FIG. 8;

FIG. 10 is a cross sectional view of the collar of the bone anchorengaging tool of FIG. 4, taken along line 10-10 of FIG. 5;

FIG. 11 is a perspective view of the rod adjusting tool of FIG. 1;

FIG. 12 is a side elevational view of the rod adjusting tool of FIG. 1;

FIG. 13 is a side elevational view in cross section of the rod adjustingtool of FIG. 1, taken along line 13-13 of FIG. 12;

FIG. 14 is a perspective view of an exemplary embodiment of an implantdriver;

FIG. 15 is a perspective view of the implant driver of FIG. 14positioned within the rod adjusting tool of FIG. 11;

FIG. 16A is a side elevational view in cross-section of the distal endof an exemplary embodiment of an instrument for adjusting a spinal rodrelative to a bone anchor;

FIG. 16B is a perspective view of the exemplary rod engaging member ofthe instrument of FIG. 16A;

FIG. 17 is a schematic of the instrument of FIG. 1 illustratingengagement of a bone anchor, rod reduction, and delivery of the closuremechanism;

FIG. 18A is a perspective view of an exemplary embodiment of aninstrument for engaging a bone anchor, illustrating the instrumentengaged to a bone anchor;

FIG. 18B is a perspective view of the instrument of FIG. 18A;

FIG. 18C is a top view of the instrument of FIG. 18A;

FIG. 18D, is a side view of the instrument of FIG. 18A, illustrating theinstrument in the open position for facilitating engagement with a boneanchor;

FIG. 18E is a side view of the instrument of FIG. 18A, illustrating theinstrument in the closed position;

FIG. 18F is a side view of the distal end of the instrument of FIG. 18A;

FIG. 19A is a side view of an exemplary embodiment of an instrument forengaging a bone anchor having an integral spring member and an integralpivot member, illustrating the instrument in the closed position;

FIG. 19B is a side view of the instrument of FIG. 19A, illustrating theinstrument in the open position;

FIG. 20A is a side view of an exemplary embodiment of an instrument forengaging a bone anchor having an integral spring member, illustratingthe instrument in the closed position;

FIG. 20B is a side view of the instrument of FIG. 20A, illustrating theinstrument in the open position;

FIG. 21 is a side view of an exemplary embodiment of an instrument forengaging a bone anchor having an integral spring member of varyingthickness and an integral pivot member, illustrating the instrument in aclosed position;

FIG. 22A is a side view of an exemplary embodiment of an instrument forengaging a bone anchor having an integral spring member and a pivotmember, illustrating the instrument in a closed position;

FIG. 22B is a cross sectional view of the instrument of FIG. 22A,illustrating the pivot members.

FIG. 23 is a perspective view of an exemplary embodiment of aninstrument for engaging a bone anchor having an integral spring memberand a pivot member; illustrating the instrument in a closed position;

FIG. 24A is a perspective view of an exemplary embodiment of a aninstrument for engaging a bone anchor, the instrument opening in adirection perpendicular to the axis of a spinal rod received by the boneanchor;

FIG. 24B is a side view of the instrument of FIG. 24A;

FIG. 24C is side view of the instrument of FIG. 24B, taken 90° from theside view of FIG. 24B;

FIG. 25A is a perspective view of an exemplary embodiment of aninstrument for engaging a bone anchor, illustrating a generally tubularstabilizing instrument positioned at the proximal end of the instrument;

FIG. 25B is a side view of the instrument of FIG. 25A;

FIG. 25C is a side view of the stabilizing instrument of FIG. 25A;

FIG. 26A is a perspective view of an exemplary embodiment of aninstrument for engaging a bone anchor, illustrating an arcuatestabilizing instrument positioned at the proximal end of the instrument;

FIG. 26B is a side view of the instrument of FIG. 26A;

FIG. 26C is a perspective view of the stabilizing instrument of FIG.26A;

FIG. 26D is a side view of the stabilizing instrument of FIG. 26A

FIG. 27A is a side view of an exemplary embodiment of an instrument foradjusting a spinal rod relative to a bone anchor, illustrating a rodadjusting tool positioned within a bone anchor engaging tool having apair of integral springs;

FIG. 27B is a side view of the instrument of FIG. 27A;

FIG. 27C is a side view in cross section of the instrument of FIG. 27Ataken along the lines A-A of FIG. 27B;

FIGS. 27D and 27E are top and side views of the bone anchor engagingtool of FIG. 27A;

FIG. 27F is a side view in cross section of the bone anchor engagingtool of FIG. 27A taken long the line B-B of FIG. 27E;

FIG. 27G is a perspective view of the proximal component of the rodadjusting tool of FIG. 27A;

FIG. 27H is a side view of the proximal component of the rod adjustingtool of FIG. 27A;

FIG. 27I is a side view in cross section of the proximal component ofthe rod adjusting tool of FIG. 27A taken along the line B-B of FIG. 27H;

FIG. 27J is a perspective view of the distal component of the rodadjusting tool of FIG. 27A;

FIG. 27K is a side view of the distal component of the rod adjustingtool of FIG. 27A; and

FIG. 27L is a side view in cross section of the distal component of therod adjusting tool of FIG. 27A taken along the line A-A of FIG. 27K.

DETAILED DESCRIPTION

Certain exemplary embodiments will now be described to provide anoverall understanding of the principles of the structure, function,manufacture, and use of the instruments disclosed herein. One or moreexamples of these embodiments are illustrated in the accompanyingdrawings. Those of ordinary skill in the art will understand that theinstruments specifically described herein and illustrated in theaccompanying drawings are non-limiting exemplary embodiments and thatthe scope of the present invention is defined solely be the claims. Thefeatures illustrated or described in connection with one exemplaryembodiment may be combined with the features of other embodiments. Suchmodifications and variations are intended to be included within thescope of the present invention.

The articles “a” and “an” are used herein to refer to one or to morethan one (i.e. to at least one) of the grammatical object of thearticle. By way of example, “an element” means one element or more thanone element.

The term “distal” as used herein with respect to any component orstructure will generally refer to a position or orientation that isproximate, relatively, to the bone surface to which a bone anchor is tobe applied. Conversely, the term “proximal” as used herein with respectto any component or structure will generally refer to a position ororientation that is distant, relatively, to the bone surface to which abone anchor is to be applied.

The terms “comprise,” “include,” and “have,” and the derivativesthereof, are used herein interchangeably as comprehensive, open-endedterms. For example, use of “comprising,” “including,” or “having” meansthat whatever element is comprised, had, or included, is not the onlyelement encompassed by the subject of the clause that contains the verb.

FIGS. 1-3 illustrate an exemplary embodiment of an instrument 10 forengaging an implant, such as a bone anchor, and positioning a fixationelement, such as a spinal rod, relative to the bone anchor. Theexemplary instrument 10 may include an implant (e.g., bone anchor)engaging tool 12 for engaging at least a portion of an implant such as abone anchor. The exemplary bone anchor engaging tool 12 is particularsuited for engaging the proximal end of a pedicle screw, although oneskilled in the art will appreciate that the exemplary bone anchorengaging tool 12 may be employed with any type of bone anchor. Theexemplary instrument 10 may further include a rod adjustment tool 14that is connectable to the bone anchor engaging tool 12 and may beaxially adjustable relative to the bone anchor engaging tool 12. Theexemplary rod adjustment tool 14 may be advanced axially to position aspinal rod relative to a bone anchor engaged by the bone anchor engagingtool 12. For example, the rod adjustment tool 14 may be employed toreduce a spinal rod into the rod receiving portion of a pedicle screwthat is engaged by the bone anchor engaging tool 12. Although theexemplary instrument 10 is described primarily in connection with spinalapplications, one skilled in the art will appreciate that the exemplaryinstrument 10, as well as the other exemplary embodiments describedbelow, may be used to engage any type of bone anchor or other implantand/or to position any type of fixation element relative to a boneanchor.

Referring to FIGS. 4-9, the exemplary bone anchor engagement tool 10includes a first jaw member 18A and a second jaw member 18B which cancooperate to engage an implant such as a bone anchor. The first jawmember 18A and the second jaw member 18B, in the exemplary embodiment,are identical in construction and, accordingly, features of the firstjaw member 18A discussed below and illustrated in the FIGURES may alsobe present in the second jaw member 18B. The first jaw member 18A andthe second jaw member 18B each have a proximal end 20A,B and a distalend 22A,B spaced apart approximately a length L, indicated by arrow L inFIG. 5, from the proximal end 20A,B. The jaw members 18A,B have aninterior surface 19A,B and an exterior surface 21A,B. The jaw members18A,B preferably have a length L that is sufficient to span from a skinincision in a patient at the proximal end 20A,B to proximate a vertebraof the patient at the distal end 22A,B thereof. The jaw members 18A,Bmay be constructed from any biocompatible or sterilizable material,including a metal such as stainless steel, or a polymer.

The first jaw member 18A may be pivotally connected to the second jawmember 18B at pivot points 24A,B that are aligned along a pivot axis 26.The pivot axis 26, in the illustrated exemplary embodiment, is orientedgenerally perpendicular to the longitudinal axis 28 of the bone anchorengaging tool 12. The pivot axis 26, in the exemplary embodiment, ispositioned proximate the distal ends 22A,B of the jaw members 18A,B,e.g., closer to the distal ends 22A,B of the jaw members 18A,B than theproximal ends 20A,B of the jaw members 18A,B, although the pivot access26 may be located anywhere along the length of the jaw members.Manipulation of the proximal ends 20A,B of the first jaw member 18A,Bcauses the distal ends 22A,B to rotate about the pivot points 24A,B. Forexample, in the exemplary embodiment, compressing the proximal ends20A,B towards one another, as indicated by arrows 30A,B, causes thedistal ends 22A,B to rotate from an approximately closed position inwhich the jaw members are proximate one another, as indicated by arrows32A,B, to an open position in which the jaw members are displaced fromone another. FIGS. 4-6 illustrate the jaw members 18A,B in theapproximately closed position. In the approximately closed position,distal ends 22A,B of the jaw members 18A,B may be separated a distance Dthat is approximately equal to or less than the extent of the portion ofthe implant to be engaged by the bone anchor engagement tool 12 tofacilitate engagement of an implant when the distal ends 22A,B of thejaw members 18A,B are in the approximately closed position. For example,in the exemplary embodiment, the distance D may be approximately equalto or less than the outer diameter of the rod receiving portion of apedicle screw. In the exemplary embodiment, axially extending contactsurfaces 34A,B define the distance D by limiting the motion of thedistal ends 22A,B towards one another. In the open position, the distalends 22A,B may be displaced a distance greater than distance D tofacilitate positioning of the distal ends 22A,B about the implant.

The jaw members 18A,B may be coupled together by one or more pins 35that may be aligned with and define the pivot axis 26 about which thejaw members 18A,B rotate. The jaw members 18A,B, when pivotallyconnected, may form an annular collar 40 that is intersected by thepivot axis 26. For example, each jaw member 18A,B may include an arcuatesection 42A,42B that may engage to form collar 40. Each arcuate section42A,B may include a pair of spaced apart tabs 44A,B and 48A,B eachhaving an opening 46 formed therein for receiving a pin 35A,B. When thejaw members 18A,B are engaged, the tabs 44A and 48B engage to form anopening 46A and tabs 44B and 48A engage to form an opening 46B. Eachengaged pair of tabs are radially spaced apart from one another and therespective openings 46A,B are aligned to define the pivot axis 26.

The bone anchor engagement tool 12 may include a biasing mechanismcoupled to the jaw members 18A,B to bias the distal ends 22A,B to theapproximately closed position. The biasing mechanism may be, forexample, one or more springs positioned between the jaw members 18A,B.The spring(s) may a coiled spring, a leaf spring, or any other suitablespring. In the exemplary embodiment, two pairs of coiled springs 36 arepositioned between the jaw members 18A,B approximate the pivot axis 26.One or more bores 38 may be provided in the jaw members 18A,18B to seatthe springs. The number, location, and structure of the springs may bevaried depending on, for example, the amount of biasing force desired.

The jaw members 18A,B may be spaced apart a distance to define anopening therebetween that may be sized and shaped to facilitate thedelivery of an implant, such as a component of a bone anchor, or aninstrument, such as the rod adjusting tool 14, through the opening. Forexample, in the illustrated exemplary embodiment, the collar 40 isgenerally annular in shape and has a diameter, indicated by arrow X inFIG. 10, that is greater than the extent of an implant or instrument tobe delivered through the bone anchor engaging tool 12. In the exemplaryembodiment, for example the diameter X of the collar may be greater thanthe diameter of the rod adjusting tool 14 and the closure mechanism ofthe bone anchor. Likewise, the distance D between the distal ends 22A,B,in the approximately closed position, may be greater than the extent ofan implant or instrument to be delivered through the bone anchorengaging tool 12.

The bone anchor engaging tool 12 may include an adjustment mechanismthat facilitates the adjustment of a second instrument, such as, forexample, the rod adjusting tool 14, along the longitudinal axis 28 ofthe tool 12. In the illustrated exemplary embodiment, for example,internal threads 50A,B are formed on the interior surface 19A,B forengaging mating external threads formed on the second instrument. Theinternal threads 50A,B are preferably located proximal to the pivot axis26. The adjustment mechanism is not limited to threads; one skilled inthe art will appreciate that other structures that facilitate axialadjustment of a second instrument may be employed, including, forexample, slot(s) or groove(s) formed in the jaw members to receivepin(s) or other structures provided on the second instrument or pin(s)or other projections provided on the interior of the jaw members 18A,Bthat seat within groove(s) or slot(s) provided on the second instrument.

Although the exemplary embodiment includes an internal adjustmentmechanism, e.g., threads 50A,B, one skilled in the art will appreciatethat the tool 12 may alternatively include an external adjustmentmechanism, in which case the second instrument may be advanced about(e.g., exterior to) the bone anchor engaging tool.

The distal end 22 A,B on one or both of the jaw members 18A,B mayinclude an implant engagement mechanism that provides a releasableconnection between the distal end(s) and the implant. For example, theimplant engagement mechanism may be one or more projections that extendfrom an interior surface 52 of a distal end 22. In the illustratedexemplary embodiment, for example, each distal end 22A,B includes acylindrical pin 54A,B extending from an interior surface thereof. Thecylindrical pins 54A,B may be sized to engage swage holes provided inexterior surface of the rod receiving portion of a pedicle screw, forexample. Alternatively, the implant engagement mechanism may be one ormore ridges provided on one or both interior surfaces 52A,B tofacilitate gripping of the implant. As discussed below in connectionwith the embodiment illustrated in FIG. 16, the implant engagementmechanism may be an arcuate rim that is configured to seat within anarcuate groove provided in exterior surface of the rod receiving portionof a pedicle screw.

FIGS. 11-13 illustrate an exemplary embodiment of a rod adjusting tool14 that is connectable to the bone anchor engaging tool 12 describedabove and as illustrated in FIGS. 1-3. The rod adjusting tool 14includes a proximal end 60 and a distal end 62 spaced apart a length L₂from the proximal end 60. The rod adjusting tool 14, in the exemplaryembodiment, is generally tubular in shape and has an approximatelycircular cross-section. One skilled in the art will appreciate that therod adjusting tool 14 have other cross-sectional configurations,including, for example, elliptical or rectilinear. The rod adjustingtool 14 preferably has a length L₂ that is sufficient to span from askin incision in a patient at the proximal end 60 to proximate avertebra of the patient at the distal end 62 thereof. The rod adjustingtool 14 may be constructed from any biocompatible material, including ametal such as stainless steel, or a polymer.

The rod adjusting tool 14 includes an inner lumen 64 that extends fromthe proximal end 60 to the distal end 62 along the longitudinal axis 66.The lumen 64 may be sized and shaped to allow an implant, such as acomponent of the bone anchor, or another instrument pass therethrough.For example, in the illustrated exemplary embodiment, the lumen 64 hasan inner diameter D2 that is greater than or approximately equal to theclosure mechanism of the bone anchor engaged by the bone anchor engagingtool 12 and that is greater than or approximately equal to an instrumentfor securing the closure mechanism to the bone anchor, such as theexemplary driver illustrated in FIG. 14.

The rod adjusting tool 14 preferably has an outer diameter D₃ that isless than or approximately equal to the diameter of the collar 40 of thebone anchor engaging tool 12.

As discussed above, the rod adjusting tool 14 may be connectable to andaxial adjustable relative to the bone anchor engaging tool 12. In theexemplary embodiment, for example, the rod adjusting tool 14 isadjustable along the longitudinal axis of the bone anchor engaging tool12 from a first, proximal position, in which the distal end 62 of therod adjustment tool 14 is displaced from the distal ends 22A,B of thejaw members 18A,B, to a second, distal position in which the distal end62 of the rod adjustment tool 14 is proximate, relatively, to the distalends 22A,B of the jaw members 18A,B. During axial advancement from thefirst position to the second position, the distal end 62 of the rodadjusting tool 14 can engage the spinal rod, or other fixation element,and advance the spinal rod distally relative to the bone anchor. In theexemplary embodiment, the diameter of the rod adjusting tool 14 at thedistal end 62 may be greater than outer diameter of the rod receivingportion of the bone anchor such that the distal end 62 may slide over atleast a portion of the rod receiving portion of the bone anchor to seatthe rod in the bone anchor. The distal end 62 of the rod adjusting tool14 may be contoured to seat against the spinal rod and facilitateadvancement of the rod by the rod adjusting tool 14.

As discussed above, the rod adjusting tool 14 may have external threads68 that matingly engage internal threads 50A,50B of the jaw members18A,B to facilitate axial adjustment of the rod adjusting tool 14 andprovide mechanical advantage. One skilled in the art will appreciatethat other adjustment mechanisms are possible, as discussed above. Theproximal end 60 of the rod adjusting tool 14 may include a handle 70 tofacilitate rotation of the rod adjusting tool 14 relative to the boneanchor engaging tool 12.

FIGS. 14 and 15 illustrate an exemplary embodiment of a driver 70 forsecuring a closure mechanism, or other component of a bone anchor, tothe bone anchor. The driver 70 may have a proximal end 72 including ahandle and a distal end 74 for engaging the closure mechanism. Any typeof closure mechanism can be employed, including internally and/orexternally threaded caps, twist-in caps, and multi-component caps. Thedriver 70 may be axially advanced through the lumen 64 of the rodadjustment tool 14 such that the distal end 74 of the driver 70 isadvanced distal to the distal end 62 of the rod adjusting tool 14, asillustrated in FIG. 14. The driver 70 and the rod adjusting tool 14 mayinclude an adjustment mechanism, analogous to one or more of theadjustment mechanisms described above, to facilitate axial adjustment ofthe driver 70 relative to the rod adjusting tool 14. For example, thedriver 70 may include external threads for engagement with internalthreads provided within the lumen 64 of the rod adjusting tool 14.

FIGS. 16A and 16B illustrate an alternative exemplary embodiment of theinstrument 10, in which a rod engaging member 90 is positioned distal tothe distal end 62 of the rod adjustment tool. The rod engaging member90, in the exemplary embodiment, includes an annular ring 91 and one ormore axially oriented extensions 92 that extend distally from theannular ring 91. In the exemplary embodiment, for example, the rodengaging member 90 includes a pair of opposed extensions 92A,B. Theextensions 92A,B may be sized to fit within the rod receiving slot 104of the rod receiving portion 102 of the exemplary bone anchor 100. Thedistal end of the extensions 92 can engage the spinal rod 110 duringaxial advancement of the rod engaging member 90 by the rod adjustingtool 14.

The rod engaging member 90 may be rotatably fixed with respect to therod adjusting tool 14 such that during rotation of the rod adjustingtool 14, the rod engaging member 90 is inhibited from rotating. Forexample, one or more guide pins 93 may be provided on the annular ring91 that may seat within one or more axially oriented grooves provided onthe interior surface of the jaw members 18A,B. In this manner, the rodengaging member 90 may be adjusted axially by the rod adjusting tool 12with limited, if any rotation of rod engaging member 90. A biasingmechanism may be provided to bias the rod engaging member 90 axially inthe proximal direction. For example, one or more axially orientedsprings 96 may be provided between the annular ring 91 and the distalends 22A,B of the jaw members 18A,B.

In the exemplary embodiment illustrated in FIGS. 16A and 16B, theimplant engagement mechanism provided on the distal ends 22A,B of thejaw members 18A,B may be an arcuate rim 110A,B that is configured toseat within arcuate grooves 122A,B provided in the exterior surface ofthe rod receiving portion 102 of the bone anchor 100.

In one exemplary method of operation, the bone anchor engaging tool 12may be coupled to an exemplary bone anchor 100 by rotating the distalends 22A,B of the jaw members 18A,B to the open position, advancing thedistal ends 22A,B of the jaw members 18A,B about the bone anchor, androtating the distal ends 22A,B of the jaw members 18A,B to theapproximately closed position such that the distal ends 22A,B of the jawmembers 18A,B engage the side walls of the rod receiving portion 102 ofthe bone anchor, as illustrated in FIG. 17. Engagement of the boneanchor engaging tool 12 to the bone anchor 100 can capture the rod 110between the jaw members 18 A,B and between the collar 40 and the boneanchor 100. The rod adjusting tool 14 may be advanced axially, byrotating the proximal end 60 of the rod adjusting tool 14, such that thedistal end 62 of the rod adjusting tool 14 engages the spinal rod 110and advances the spinal rod 110 distally in the direction of the boneanchor 100. The rod adjusting tool 14 may be advanced distally to seatthe rod 110 in the rod receiving slot 104 of the bone anchor 100. Thedriver 70 may be employed to position a closure mechanism, such as anexternally threaded cap 106, within the rod receiving slot 104 tothereby capture the rod 110 in the rod receiving slot.

In one exemplary embodiment, the driver 70 and closure mechanism may bepositioned within the rod adjusting tool 14 during reduction of thespinal rod 110. For example, the driver 70 first may be positionedwithin the lumen 64 of the rod adjusting tool 14. The distal end 74 ofthe driver 70 may be advanced to the second position to engage theclosure mechanism. The distal end 74 of the driver 70 and the closuremechanism may be adjusted to the first position, in which the closuremechanism is within the lumen 64 of the rod adjusting tool 14. The rodadjusting tool may then be coupled to the bone anchor engaging tool 12and advanced to reduce the spinal rod, while the distal end 74 of thedriver 70 and the closure mechanism are within the lumen 64 of the rodadjusting tool 14. Once the rod 110 is seated, the distal end 72 of thedriver 70 may be advanced to secure the closure mechanism to the boneanchor 100.

In other exemplary embodiments, the driver 70 and the closure mechanismmay be positioned within the rod adjusting tool 14 after reduction ofthe spinal rod 110.

The bone anchor engaging tool 12 may be introduced through a minimallyinvasive incision and/or through an open incision. In minimally invasiveapplications, the tool 12 may be introduced through a port or canulla ordirectly through the minimally invasive incision. The tool 12 may beused to create a minimally invasive pathway from the skin incision tothe bone anchor for the delivery of implants or secondary instruments.

FIGS. 18A-18F illustrate an another exemplary embodiment of a boneanchor engaging tool 212 for engaging a bone anchor 100 or otherimplant. The exemplary bone anchor engaging tool 212 may be used with arod adjustment tool, such as rod adjustment tool 14 described above,with a driver, such as driver 70 described above, or with otherinstruments, as described in more detail below.

The exemplary bone anchor engaging tool 212 includes a first jaw member218A and a second jaw member 218B which can cooperate to engage animplant such as a bone anchor. The first jaw member 218A and the secondjaw member 218B may be analogous in construction, except as discussedbelow, to the first jaw member 18A and the second jaw member 18Bdescribed above in connection with bone anchor engagement tool 2. Thefirst and second jaw members 218A,B may be integrally connected by apair of opposed integral spring members 202A, 202B located proximal tothe distal ends 222A, 222B of the first and second jaw members 218A,218B. Manipulation of the proximal ends 220A, 220B of the first andsecond jaw members 218A, 218B may cause each of the distal ends 222A,22B to rotate about the pair of opposed spring members 202A, 202B. Forexample, in the exemplary embodiment, compressing proximal ends 220A,220B towards one another causes the distal ends 222A, 222B to rotatefrom an approximately closed position in which the jaw members areproximate one another, as illustrated in FIGS. 18A, 18B, 18E and 18F toan open position in which the distal end 222A, 222B are displaced fromone another, as illustrated in FIG. 18D.

In the exemplary embodiment, each of the integral spring members 202A,202B is generally arcuate in shape and spans between the first jawmember 218A and the second jaw member 218B. The properties of eachspring member 202, for example the stiffness of the spring, may bevaried by adjusting the axial thickness t of the spring member 202and/or the radial width r of the spring member 202. For example, anadjustment of the axial thickness of the spring member 202 can result inan exponential adjustment of the stiffness of the spring member 202 andadjustment of the radial width of the spring member 202 can result in alinear adjustment of the stiffness of the spring member 202. In certainembodiments, including the embodiment illustrated in FIGS. 18A-18F, eachspring member 202 is generally uniform in cross section, e.g. has agenerally constant thickness and width along its arcuate length. Inother exemplary embodiments, the cross section of the springs may varyalong its length to vary the stiffness or other properties of the springmember 202B. Referring to FIG. 21, for example, the thickness t of thespring member 202B varies along the arcuate length of the spring member202B, which can result in an exponential change in stiffness.

Referring to FIGS. 18A-18F, the pair of opposed integral spring members202A, 202B of the exemplary bone anchor engaging tool 212 may bias thedistal ends 222A, 22B to the closed position as illustrated in FIGS.18A, 18B, 18E and 18F. In the exemplary embodiment, a retaining collar204 may be positioned at least partially about the first jaw member 218Aand the second jaw member 218B to inhibit separation of the proximal end220A of first jaw member 218A and the proximal end 220B of the secondjaw member 218B from one another.

In the exemplary embodiment, the first jaw member 218A, the second jawmember 218B, and the pair of spring members 202A, 202B may be integrallyformed, e.g. may be of single piece construction from one commoncomponent. For example, the first jaw member 218A, the second jaw member218B, and the pair of spring members 202A, 202B may be manufactured froma tubular stock component using conventional lathe turning operationsfollowed by wire EDM cutting procedures.

The bone anchor engaging tool 212 may include a pair of opposed pivotmembers 206A,B each pivot member 206 positioned adjacent (proximal ordistal) a respective one of the spring members 202A, 202B to provide acontact surface about which the distal ends 222A, 222B of the first jawmember 218A and the second jaw member 218B can rotate. In theillustrated embodiment, for example, the pivot members 206A, 206B caneach include a generally planar contact surface 208. A portion of one ofthe jaw members 218A, 218B can bear against each planar contact surface208 to create a pivot axis about which the first jaw member 218A and thesecond jaw member 218B can rotate. In certain embodiments, such as theillustrated embodiment, the pivot members 206 may be separate componentsfrom the instrument (jaw members and spring members) and may be coupledto the instrument by, for example, welding. In other embodiments, forexample the embodiment illustrated in FIGS. 19A and 19B, the pivotmembers 206 may be integrally formed with the bone anchor engaging tool212. In other embodiment, for example the embodiment illustrated inFIGS. 20A and 20B, pivot members may not be provided.

Referring to FIGS. 22A-22B, in certain exemplary embodiments, each ofthe pivot members 206 may be a plate 207 having a projection, forexample, a pivot pin 209, that can be connected to the bone anchorengaging tool 212 by, for example, welding, proximal to the springmembers 202. In the illustrated embodiment, for example, each plate may207 may be connected to the first jaw member 218A and each pivot pin 209may be received through an opening provided in the second jaw member218B. The pivot pins 209 may be aligned to provide a pivot axis aboutwhich the first jaw member 218A and the second jaw member 218B mayrotate to provide single degree of freedom motion.

Referring to FIG. 23, in certain exemplary embodiments, the motion ofthe first and second jaw members 218A, 218B may be restrained by, forexample, providing a pair of opposed guide posts 211 that limit thetranslation and rotational movement of the jaw members 218. Eachguidepost 211 may be received at one end in a socket 213A provided onthe first jaw member 218A and may be received at the other end in asocket 213B provided on the second jaw member 218B. One or both of thesockets 213A, 213B may translate along the length of the guide post 211to generally restrain the motion of the first and second jaw members 218to approximately along the axis of the guide post 211.

In certain exemplary embodiment, including the embodiments describedabove, the first jaw member and the second jaw member rotate about anaxis that is parallel to the longitudinal axis of the spinal rod. Inother embodiments, the first jaw member and the second jaw member rotateabout an axis that is perpendicular to the longitudinal axis of thespinal rod. Referring to FIGS. 24A-24B, for example, the first jawmember 218A and the second jaw member 218B rotate between a closedposition, illustrated in FIG. 24C, and an open position in a direction(generally along arrows R) parallel to the longitudinal axis L of thespinal rod 110. In such embodiments, the slots 225A,B provided in eachof the distal ends 222A, B of the first and second jaw members 218A,218B remain oriented to permit the spinal rod 110 to be positionedbetween the distal ends 222A, B of the first and second jaw members218A, 218B.

The instruments for engaging a bone anchor disclosed herein, includinginstrument 12 and bone anchor engaging tool 212, may include astabilizing instrument 300 positionable between the first jaw member218A and the second jaw member 218B to stabilize the proximal end 220Aof the first member 218A and the proximal end 220B of the second jawmember 218B. Referring to FIGS. 25A-C, for example, the stabilizinginstrument 300 may be sized in inhibit the proximal end 220A of thefirst member 218A and the proximal end 220B of the second jaw member218B from moving towards one another thereby providing torsional androtational stability to the bone anchor engaging tool 212 when the boneanchor engaging tool 212 engages a bone anchor 100. In the illustratedembodiment, the stabilizing instrument 300 is generally tubular inshape. The exemplary stabilizing instrument has a central segment 302having a diameter d approximately equal to the distance between theproximal end 220A of the first member 218A and the proximal end 220B ofthe second jaw member 218B when the bone anchor engaging tool 212 is inthe closed configuration. The exemplary stabilizing instrument 300 mayinclude a proximal segment 304 having a diameter D greater that thedistance between the proximal end 220A of the first member 218A and theproximal end 220B of the second jaw member 218B (when the bone anchorengaging tool 212 is in the closed configuration) to facilitatemanipulation of the stabilizing instrument 300 relative to the boneanchor engaging tool 212. The exemplary stabilizing instrument 300 mayalso include a distal segment 306 having a reduced diameter compared tothe central segment 302 to facilitate positioning of the stabilizinginstrument 300 between the first and second jaw members 218A, 218B.

FIGS. 26A-26D illustrate another exemplary embodiment of a stabilizinginstrument 350 that is generally arcuate in shape and includes a pair ofopposed spacers 352 each sized to fit between the proximal end 220A ofthe first jaw member 218A and the proximal end 220B of the second jawmember 218B when the bone anchor engaging tool 212 engages a bone anchor100. In particular, the spacers 352 of the exemplary stabilizinginstrument 350 each may be positioned at an end of an arcuate bodyportion 354 of the stabilizing instrument 350. Each spacer 352 may havea width W approximately equal to the to the distance between theproximal end 220A of the first member 218A and the proximal end 220B ofthe second jaw member 218B when the bone anchor engaging tool 212 is inthe closed configuration.

The exemplary stabilizing instruments may be employed to stabilize thebone anchor engaging tool 212 when the instrument is engaged to a boneanchor 100. The additional stability provided by the exemplarystabilizing instruments facilitates manipulation of the bone anchor 100,and the bone (e.g., vertebra) that the bone anchor is anchored to, usingthe bone anchor engaging tool 212. In one exemplary method, the boneanchor engaging tool 212 (or bone anchor engaging tool 12) may beengaged to a bone anchor 100 anchored in a vertebra and a stabilizerinstrument may be positioned between the proximal ends 220A,B of thefirst and second jaw members 218A, 218B to stabilize the bone anchorengaging tool 212. The bone anchor engaging tool 212 then may be used tomanipulate, for example rotate, the bone anchor 100 and the vertebra inwhich the bone anchor 100 is implanted relative to the axis of thespine.

FIGS. 27A-L illustrate another exemplary embodiment of an instrument 400for engaging an implant, such as a bone anchor, and positioning afixation element, such as a spinal rod, relative to the bone anchor. Theexemplary instrument 400 may include an implant (e.g., bone anchor)engaging tool 412 for engaging at least a portion of an implant such asa bone anchor. The exemplary bone anchor engaging tool 412 isparticularly suited for engaging the proximal end of a pedicle screw,although one skilled in the art will appreciate that the exemplary boneanchor engaging tool 412 may be employed with any type of bone anchor.The exemplary instrument 410 may further include a rod adjustment tool414 that is connectable to the bone anchor engaging tool 412 and may beaxially adjustable relative to the bone anchor engaging tool 412. Theexemplary rod adjustment tool 414 may be advanced axially to position aspinal rod relative to a bone anchor engaged by the bone anchor engagingtool 412. For example, the rod adjustment tool 414 may be employed toreduce a spinal rod into the rod receiving portion of a pedicle screwthat is engaged by the bone anchor engaging tool 412.

The exemplary bone anchor engaging tool 412 of the exemplary instrument400 may be constructed in manner analogous to the bone anchor engagingtool 12 and/or the bone anchor engaging tool 212, described above. Forexample, the bone anchor engaging tool 412 may include a first jawmember 418A and a second jaw member 418B which can cooperate to engagean implant such as a bone anchor. The first jaw member 418A may beintegrally connected by a pair of opposed integral spring members 402A,402B located proximal to the distal ends 422A, 422B of the first andsecond jaw members 418A, 418B. Manipulation of the proximal ends 420A,420B of the first and second jaw members 418A, 418B causes each of thedistal ends 422A, 42B to rotate about the pair of opposed spring members402A, 402B. For example, in the exemplary embodiment, compressingproximal ends 420A, 420B towards one another causes the distal ends422A, 42B to rotate from an approximately closed position in which thejaw members are proximate one another, as illustrated in FIG. 27D, to anopen position in which the distal end 422A, 422B are displaced from oneanother.

In the illustrated embodiment, the bone anchor engaging tool 412, aswell as the rod adjustment tool 414, have a reduced axial lengthcompared to the exemplary instruments described above. In procedures inwhich multiple instruments 400 are used simultaneous, for example, aplurality of instruments 200 each placed on separate bone anchor, thisconfiguration minimizes interference between adjacent instruments 400,facilitates visualization of the surgical field, and minimizes the needfor the instruments 400 to be held by the surgeon to maintain theinstruments 400 in position.

The bone anchor engaging tool 412 may include an adjustment mechanismthat facilitates the adjustment of a second instrument, such as, forexample, the rod adjusting tool 414, along the longitudinal axis of thetool 412. In the illustrated exemplary embodiment, for example, internalthreads 450A,B are formed on the interior surface for engaging matingexternal threads formed on the second instrument.

In the exemplary embodiment, the rod adjusting tool 414 includes adistal component 419 having a rod engaging surface 421 and a proximalcomponent 423 connectable to and separable from the distal component419. In operation, rotation of the proximal component 423 causes thedistal component 419 to advance axially relative to the bone anchorengaging tool 412. In the exemplary embodiment, the distal component 419is generally tubular in shape and includes an external thread 425 formedthereon at the proximal end of the distal component 419. The distalcomponent 419 includes a pair of opposed distal legs 431A, 431B each ofwhich provides a rod engaging surface 421A, 421B at the distal endthereof. The distal component 419 can include at least one projection427 for engaging the bone engaging tool 412 to inhibit rotation of thedistal component 419 relative to the bone engaging tool 412 duringadvancement of the distal component 419. For example, the distalcomponent 419 can include a pair of opposed projections 427A, 427B thatseat within the slots 429A, 429B formed by the space between the firstjaw member 418A and the second jaw member 418B.

In the exemplary embodiment, the proximal component 423 is generallytubular in shape and includes an internal thread 433 for engaging theexternal thread 425 of the distal component 419 and an external thread435 for engaging the internal threads 450A,B formed on the interiorsurface of the bone anchor engaging tool 412. The external thread 435 ofthe proximal component 423 and the internal thread 433 of the proximalcomponent 423 may have opposite thread directions. For example, in theexemplary embodiment, the external thread 435 of the proximal component423 may be a right hand thread and the internal thread 433 of theproximal component 423 may be a left hand thread. Such an arrangementresults in the advancement of the rod adjusting tool 414 at twice thespeed of an arrangement employing a single lead thread.

While the instruments of the present invention have been particularlyshown and described with reference to the exemplary embodiments thereof,those of ordinary skill in the art will understand that various changesmay be made in the form and details herein without departing from thespirit and scope of the present invention. Those of ordinary skill inthe art will recognize or be able to ascertain many equivalents to theexemplary embodiments described specifically herein by using no morethan routine experimentation. Such equivalents are intended to beencompassed by the scope of the present invention and the appendedclaims.

What is claimed is:
 1. A spinal instrument comprising: a bone anchorengaging tool comprising a first anchor engaging member having aproximal end and a distal end a second anchor engaging member having aproximal end and a distal end, the second anchor engaging member beingpivotally connected to the first anchor engaging member at a pivotpoint, manipulation of the proximal ends of the first and second anchorengaging members causing the distal ends of the first and second anchorengaging members to rotate about the pivot point between a closedposition in which the distal ends are proximate one another and an openposition in which the distal ends are displaced from one another, thefirst and second anchor engaging members being spaced apart a distanceto form a central opening sized to receive an a spinal rod adjustingtool therein, the central opening having a central axis extending fromthe proximal ends of the first and second anchor engaging members andthe distal ends of the first and second anchor engaging members, thedistal ends of the first and second anchor anchoring members beingspaced equidistantly from the central axis in the open position, theclosed position, and during rotation between the open and closedpositions, a rod adjusting tool connectable to the bone anchor engagingtool and having a proximal end and a distal end, the rod adjustment toolpositionable within the central opening between the first and secondanchor engaging members, the rod adjusting tool being axially adjustablethrough the central opening relative to the bone anchor engaging tool toadjust a spinal rod relative to a bone anchor connected to the boneanchor engaging tool; and an adjustment mechanism to facilitate theconnection and adjustment of the rod adjusting tool relative to the boneanchor engaging tool, the adjustment mechanism comprising a threadformed on at least one of an inner surface of the first anchor engagingmember and on an inner surface of the second anchor engaging member, thethread engaging a mating thread formed on the rod adjusting tool.
 2. Thespinal instrument of claim 1, wherein the distal end of the first anchorengaging member includes a projection extending from an inner surface ofthe distal end.
 3. The spinal instrument of claim 2, wherein the distalend of the second anchor engaging member includes a projection extendingfrom an inner surface of the distal end.
 4. The spinal instrument ofclaim 1, further comprising a biasing mechanism coupled to the firstanchor engaging member and the second anchor engaging member to bias thedistal ends to the closed position.
 5. The spinal instrument of claim 4,wherein the biasing mechanism comprises at least one spring positionedbetween the first anchor engaging member and the second anchor engagingmember.
 6. The spinal instrument of claim 1, wherein the distal endswhen in the closed position are separated a distance that isapproximately equal to or less than a width or a diameter of the portionof the bone anchor.
 7. The spinal instrument of claim 1, wherein the rodadjustment tool is a cylindrical tube.
 8. The spinal instrument of claim1, wherein the rod adjustment tool includes a handle positioned at theproximal end thereof to facilitate adjustment of the rod adjustmenttool.
 9. The spinal instrument of claim 1, wherein the rod adjustmenttool includes a rod engaging member positioned at the distal end of therod adjustment tool, the rod engaging member being axially adjustableand inhibited from rotation relative to the rod adjustment tool.
 10. Thespinal instrument of claim 9, wherein the rod engaging member includesat least one axial extension having a rod engaging surface, the axialextension being sized to move within a rod receiving recess of a boneanchor connected to the bone anchor engaging tool.
 11. The spinalinstrument of claim 1, wherein the rod adjustment tool includes an innerlumen through which a closure mechanism may be delivered to a boneanchor connected to the bone anchor engaging tool.
 12. The spinalinstrument of claim 1, further comprising a stabilizing instrumentpositionable between the first anchor engaging member and the secondanchor engaging member to inhibit the proximal end of the first anchorengaging member and the proximal end of the second anchor engagingmember from moving towards one another.
 13. The spinal instrument ofclaim 12, wherein the stabilizing instrument is generally arcuate inshape and includes a pair of opposed spacers each sized to fit betweenthe proximal end of the first anchor engaging member and the proximalend of the second anchor engaging member when the bone anchor engagingtool engages a bone anchor.
 14. The spinal instrument of claim 1,further comprising a retaining collar positioned about the first anchorengaging member and the second anchor member to inhibit separation ofthe proximal end of first anchor engaging member and the proximal end ofthe second anchor engaging member from one another.
 15. A spinalinstrument comprising: a bone anchor engaging tool comprising a firstanchor engaging member having a proximal end and a distal end a secondanchor engaging member having a proximal end and a distal end, thesecond anchor engaging member being pivotally connected to the firstanchor engaging member at a pivot point, manipulation of the proximalends of the first and second anchor engaging members causing the distalends of the first and second anchor engaging members to rotate about thepivot point between a closed position in which the distal ends areproximate one another and an open position in which the distal ends aredisplaced from one another, the first and second anchor engaging membersbeing spaced apart a distance to form a central opening sized to receivean a spinal rod adjusting tool therein, the central opening having acentral axis extending from the proximal ends of the first and secondanchor engaging members and the distal ends of the first and secondanchor engaging members, the distal ends of the first and second anchoranchoring members being spaced equidistantly from the central axis inthe open position, the closed position, and during rotation between theopen and closed positions, the distal end of the first anchor engagingmember and the distal end of the second anchor engaging member eachincluding a projection extending from an inner surface of the distalend, a rod adjusting tool connectable to the bone anchor engaging tooland having a proximal end and a distal end, the rod adjustment toolpositionable within the central opening between the first and secondanchor engaging members, the rod adjusting tool being axially adjustablethrough the central opening relative to the bone anchor engaging tool toadjust a spinal rod relative to a bone anchor connected to the boneanchor engaging tool; and an adjustment mechanism to facilitate theconnection and adjustment of the rod adjusting tool relative to the boneanchor engaging tool.
 16. A spinal instrument comprising: a bone anchorengaging tool comprising a first anchor engaging member having aproximal end and a distal end a second anchor engaging member having aproximal end and a distal end, the second anchor engaging member beingpivotally connected to the first anchor engaging member at a pivotpoint, manipulation of the proximal ends of the first and second anchorengaging members causing the distal ends of the first and second anchorengaging members to rotate about the pivot point between a closedposition in which the distal ends are proximate one another and an openposition in which the distal ends are displaced from one another, thefirst and second anchor engaging members being spaced apart a distanceto form a central opening sized to receive an a spinal rod adjustingtool therein, the central opening having a central axis extending fromthe proximal ends of the first and second anchor engaging members andthe distal ends of the first and second anchor engaging members, thedistal ends of the first and second anchor anchoring members beingspaced equidistantly from the central axis in the open position, theclosed position, and during rotation between the open and closedpositions, a cylindrically shaped rod adjusting tool connectable to thebone anchor engaging tool and having a proximal end and a distal end,the rod adjustment tool positionable within the central opening betweenthe first and second anchor engaging members, the rod adjusting toolbeing axially adjustable through the central opening relative to thebone anchor engaging tool to adjust a spinal rod relative to a boneanchor connected to the bone anchor engaging tool; and an adjustmentmechanism to facilitate the connection and adjustment of the rodadjusting tool relative to the bone anchor engaging tool.
 17. The spinalinstrument of claim 16, wherein an outer surface the rod adjusting toolincludes an external thread formed thereon.
 18. The spinal instrument ofclaim 17, wherein an inner surface of the first anchor engaging memberand an inner surface of the second anchor engaging member include aninternal thread formed thereon, the external thread of the rod adjustingtool engaging the internal thread to facilitate axial adjustment of therod adjustment tool relative to the bone anchor engagement tool.